Systematics of Mielichhoferia (Bryaceae: Musci). III. Hybridization between M. elongata and M. mielichhoferiana

Allozyme variation in mixed populations of Mielichhoferia elongata and M. mielichhoferiana was investigated to determine if interspecific hybridization occurs when these two closely related species grow together. Previous research has shown that M. elongata and M. mielichhoferiana can be distinguished by three diagnostic isozyme loci (Gpi-1, Mdh-2, and Mdh-3) at which the two species do not share alleles in 32 allopatric populations from North America and Europe. The present study shows that in five populations from Colorado, Norway, and Sweden, gametophytes resulting from interspecific hybridization can be recognized by recombinant genotypes combining alleles of the otherwise diagnostic loci. A total of 32 multilocus genotypes was found among the 111 individuals sampled, of which 13 were recombinants. The frequency of recombinants ranged from 12% to 35% within populations, and all but one population contained both parental species. Moreover, recombinant genotypes could be accounted for by the allelic constitution of sympatric parents. In two of the populations, more than one hybridization event was necessary to account for the diversity of recombinant genotypes. Twenty-nine of the 32 genotypes detected in this study were restricted to one population each, two occurred in two Swedish populations separated by approximately 14 km, and one occurred in both Sweden and Norway.